Contactor,circuit breaker,solar inverter,electric meter,solar batteries
Coordination Standard: IEC 60947-2
Core Principle: The short-time delay protection time of the upper-level air circuit breaker (3WT) > the instantaneous trip time of the lower-level molded case circuit breaker, realizing precise isolation of faulty branches and avoiding system over-tripping.
| Application Scenario | Parameters of Upper-level Air Circuit Breaker (3WT2M40 ETU35WT F-4P) | Selection and Parameters of Lower-level Molded Case Circuit Breaker (Siemens 3VL Series) | Coordination Effectiveness Judgment |
| High-power Motor Circuit | Overload long-time delay: Ir = 1600A (1.0×In) | Model: 3VL2740-1AA33-0AA0 | Lower-level instantaneous trip current (3200A) < Upper-level short-time delay current (12800A) |
| (e.g., 160kW/380V motor, rated current ≈ 320A) | Short-circuit short-time delay: Isd = 8×Ir = 12800A | Rated current: 400A | Lower-level instantaneous operating time (≤ 0.02s) < Upper-level short-time delay time (0.2s) |
| Short-time delay time: 0.2s | Overload long-time delay: Ir = 320A | ✓ Full selective coordination | |
| Instantaneous protection: Off (Ii = Off) | Instantaneous trip: Ii = 10×Ir = 3200A | ||
| Trip type: TMD | |||
| General Power Circuit | Overload long-time delay: Ir = 1600A | Model: 3VL2763-1AA33-0AA0 | Lower-level instantaneous current (4800A) < Upper-level short-time delay current (9600A) |
| (e.g., water pumps, fans, total current ≈ 600A) | Short-circuit short-time delay: Isd = 6×Ir = 9600A | Rated current: 630A | Lower-level operating time < Upper-level short-time delay time |
| Short-time delay time: 0.3s | Overload long-time delay: Ir = 600A | ✓ Full selective coordination | |
| Instantaneous protection: Off | Instantaneous trip: Ii = 8×Ir = 4800A | ||
| Trip type: TMD | |||
| Lighting/Socket Distribution Circuit | Overload long-time delay: Ir = 1600A | Model: 3VL2732-1AA33-0AA0 | Lower-level instantaneous current (3000A) < Upper-level short-time delay current (8000A) |
| (Three-phase four-wire system, total current ≈ 250A) | Short-circuit short-time delay: Isd = 5×Ir = 8000A | Rated current: 320A | Operating time meets level difference |
| Short-time delay time: 0.2s | Overload long-time delay: Ir = 250A | ✓ Full selective coordination | |
| Instantaneous protection: Off | Instantaneous trip: Ii = 12×Ir = 3000A | ||
| Trip type: TMD | |||
| Emergency Power Supply Circuit | Overload long-time delay: Ir = 1600A | Model: 3VL2750-1AA33-0AA0 | Lower-level instantaneous current < Upper-level short-time delay current |
| (e.g., EPS/UPS output, current ≈ 400A) | Short-circuit short-time delay: Isd = 7×Ir = 11200A | Rated current: 500A | Upper-level instantaneous current (16000A) is much larger than that of the lower level; upper-level operates only in case of severe short circuit |
| Short-time delay time: 0.4s | Overload long-time delay: Ir = 400A | ✓ Selective coordination + backup protection | |
| Instantaneous protection: Ii = 10×In = 16000A | Instantaneous trip: Ii = 10×Ir = 4000A | ||
| Trip type: TMD |
Notes on Coordination Design
- Setting of Upper-level Instantaneous Protection: For branch short-circuit faults, it is recommended to turn off the instantaneous protection of 3WT (Ii = Off) and retain only the short-time delay protection; the instantaneous protection shall be enabled as backup only when bus short circuit occurs in the system (short-circuit current ≥ 12800A).
- Cable Cross-section Matching: The cable between the upper and lower-level circuit breakers shall meet the “short-circuit withstand capacity” to prevent cable burnout before the circuit breaker operates.
- Ambient Temperature Correction: When the temperature inside the distribution cabinet exceeds 40℃, derating of the rated current of the circuit breaker is required (derating by 1% for every 1℃ rise) to ensure stable protection characteristics.
- Selection of Lower-level Trip Type: TMD trip unit (thermal-magnetic trip) is preferred for motor circuits, and MIC trip unit (electronic trip) can be selected for lighting circuits to improve protection accuracy.
